This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. PLP-containing enzymes constitute a very important class of enzymes involved in a variety of essential metabolic processes. These pathways are well conserved among living organisms. PLP-containing enzymes also exhibit well conserved sequences and folds. Not much is known about the architecture of archeal homologs of PLP-containing enzymes but it is known that sequence conservation is typically low among them. Following evolution, eurobacteria diverged from archea along time ago. We are interested in learning whether the fold of PLP-containing enzymes is also conserved. If that were the case, we are interested in establish the residues that determine the fold of these enzymes.